157,217 research outputs found
Emptying and Refilling of Slime Glands in Atlantic (\u3cem\u3eMyxine glutinosa\u3c/em\u3e) and Pacific (\u3cem\u3eEptatretus stoutii\u3c/em\u3e) Hagfishes
Hagfishes are known for their unique defensive slime, which they use toward off gill-breathing predators. Although much is known about the slime cells (gland thread cells and gland mucous cells), little is known about how long slime gland refilling takes, or how slime composition changes with refilling or repeated stimulation of the same gland. Slime glands can be individually electrostimulated to release slime, and this technique was used to measure slime gland refilling times for Atlantic and Pacific hagfish. The amount of exudate produced, the composition of the exudate and the morphometrics of slime cells were analyzed during refilling, and as a function of stimulation number when full glands were stimulated in rapid succession. Complete refilling of slime glands for both species took 3â4 weeks, with Pacific hagfish achieving faster absolute rates of exudate recovery than Atlantic hagfish. We found significant changes in the composition of the exudate and in the morphometrics of slime cells from Pacific hagfish during refilling. Over successive stimulations of full Pacific hagfish glands, multiple boluses of exudate were released, with exudate composition, but not thread cell morphometrics, changing significantly. Finally, histological examination of slime glands revealed slime cells retained in glands after exhaustion. Discrepancies in the volume of cells released suggest that mechanisms other than contraction of the gland musculature alone may be involved in exudate ejection. Our results provide a first look at the process and timing of slime gland refilling in hagfishes, and raise new questions about how refilling is achieved at the cellular level
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Interactivity, the global conversation and World Service research: Digital China
This paper examines the relationship between a broadcasterâs research methods and aspects of the environment in which it operates, specifically its accountability to its funders and the growth of interactivity by its users. It is concerned with (1) how the BBC World Serviceâs funding by the UK governmentâs Foreign & Commonwealth Office (FCO) means that it has to account for its activities to some extent in terms of the global conversation which it fosters; and (2) how the recent growth of interactive and social media enhances possibilities for worldwide engagement and conversation, but also increases the complexities of measurement. This is because users are dispersed across the globe (they are no longer confined to a geographical area of radio reception) and they are interactive: instead of merely listening or viewing, they talk back to the BBC, and they talk with one another. New tools and techniques are needed to measure these new flows and forms of interaction (and they also beg new professional and organisational practices). In a case study of the BBCâs Chinese service, the paper explores what the BBC knows of its audience or users; and, in a content analysis of online forums, it explores some of the issues and possibilities that arise in researching online interaction, the sort of research data and analysis that might be seen as necessary in the context of organisational accountability and the emerging interactive media environment
Multi-Thread Hydrodynamic Modeling of a Solar Flare
Past hydrodynamic simulations have been able to reproduce the high
temperatures and densities characteristic of solar flares. These simulations,
however, have not been able to account for the slow decay of the observed flare
emission or the absence of blueshifts in high spectral resolution line
profiles. Recent work has suggested that modeling a flare as an sequence of
independently heated threads instead of as a single loop may resolve the
discrepancies between the simulations and observations. In this paper we
present a method for computing multi-thread, time-dependent hydrodynamic
simulations of solar flares and apply it to observations of the Masuda flare of
1992 January 13. We show that it is possible to reproduce the temporal
evolution of high temperature thermal flare plasma observed with the
instruments on the \textit{GOES} and \textit{Yohkoh} satellites. The results
from these simulations suggest that the heating time-scale for a individual
thread is on the order of 200 s. Significantly shorter heating time scales (20
s) lead to very high temperatures and are inconsistent with the emission
observed by \textit{Yohkoh}.Comment: Submitted to Ap
How quickly can we sample a uniform domino tiling of the 2L x 2L square via Glauber dynamics?
TThe prototypical problem we study here is the following. Given a square, there are approximately ways to tile it with
dominos, i.e. with horizontal or vertical rectangles, where
is Catalan's constant [Kasteleyn '61, Temperley-Fisher '61]. A
conceptually simple (even if computationally not the most efficient) way of
sampling uniformly one among so many tilings is to introduce a Markov Chain
algorithm (Glauber dynamics) where, with rate , two adjacent horizontal
dominos are flipped to vertical dominos, or vice-versa. The unique invariant
measure is the uniform one and a classical question [Wilson
2004,Luby-Randall-Sinclair 2001] is to estimate the time it takes to
approach equilibrium (i.e. the running time of the algorithm). In
[Luby-Randall-Sinclair 2001, Randall-Tetali 2000], fast mixin was proven:
for some finite . Here, we go much beyond and show that . Our result applies to rather general domain
shapes (not just the square), provided that the typical height
function associated to the tiling is macroscopically planar in the large
limit, under the uniform measure (this is the case for instance for the
Temperley-type boundary conditions considered in [Kenyon 2000]). Also, our
method extends to some other types of tilings of the plane, for instance the
tilings associated to dimer coverings of the hexagon or square-hexagon
lattices.Comment: to appear on PTRF; 42 pages, 9 figures; v2: typos corrected,
references adde
Evolution of Conversations in the Age of Email Overload
Email is a ubiquitous communications tool in the workplace and plays an
important role in social interactions. Previous studies of email were largely
based on surveys and limited to relatively small populations of email users
within organizations. In this paper, we report results of a large-scale study
of more than 2 million users exchanging 16 billion emails over several months.
We quantitatively characterize the replying behavior in conversations within
pairs of users. In particular, we study the time it takes the user to reply to
a received message and the length of the reply sent. We consider a variety of
factors that affect the reply time and length, such as the stage of the
conversation, user demographics, and use of portable devices. In addition, we
study how increasing load affects emailing behavior. We find that as users
receive more email messages in a day, they reply to a smaller fraction of them,
using shorter replies. However, their responsiveness remains intact, and they
may even reply to emails faster. Finally, we predict the time to reply, length
of reply, and whether the reply ends a conversation. We demonstrate
considerable improvement over the baseline in all three prediction tasks,
showing the significant role that the factors that we uncover play, in
determining replying behavior. We rank these factors based on their predictive
power. Our findings have important implications for understanding human
behavior and designing better email management applications for tasks like
ranking unread emails.Comment: 11 page, 24th International World Wide Web Conferenc
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